Target practice requires the participant to fire projectiles at a specified target, typically to improve the participant's aim. Conventionally, persons are trained in the use of firearms at firing ranges by shooting at cardboard or paper targets. Professionals who are required to be skilled in the use of firearms, such as soldiers and police officers, also routinely shoot a targets to maintain their skills. Accuracy is usually assessed by either physically accessing the target and recording the scores after a shooting session, or by viewing the target using a spotting scope.
Various approaches to electronically scoring projectile targets are known in the art. Conventionally, four or more accelerometers or shock or vibration sensors are mounted on a steel plate target to detect a shockwave in the target material. The run-time difference of the shockwave between the different sensors is used to calculate the point of impact of the projectile on the target.
The use of accelerometers as sensors in the prior art has a number of disadvantages. First, because accelerometers measure the intensity of the impact sensor received from the sensors, the system can only be tuned to detect a specific caliber of ammunition because different calibers have very different impact intensities. However, even the same caliber of ammunition can have significant impact intensity variation from cartridge to cartridge, which can adversely affect impact location determination accuracy. Second, accelerometers are relatively expensive, which limits the number that can be economically employed on a target, thereby decreasing the accuracy of the impact location calculation. Third, accelerometers are fragile, to the extent that if a bullet hits the target material where a sensor is located, the sensor is likely to be destroyed and/or detached from the target material. As a result, accelerometers have to be located well away from the desired central aim point on the target material where most bullet impacts will occur, thereby decreasing the accuracy of the impact location calculation. Furthermore, targets with accelerometers as sensors can only be economically utilized by a reasonably skilled shooter who is unlikely to inadvertently shoot a sensor.
Other prior art targets use piezoelectric or vibration sensors to determine location using time difference of arrival (TDOA). When bullet impacts one face of a steel target plate, an initial vibration wave is generated. Once the vibration wave reaches the opposite face of the steel target plate, a second reflection vibration wave is generated. The existence of multiple vibration waves generates an undulatory disturbance corresponding to the combination of two or more elementary waves of similar wavelengths with similar amplitude and relative difference of phase. The sum of these elementary waves produces a resulting wave as shown in FIG. 16.
This resulting wave changes between double or zero amplitude relative to the initial vibration wave generated by the bullet impact. If the resulting wave has zero amplitude as it travels over a piezoelectric or vibration sensor, the sensor will not detect any vibration (amplitude) until the next wave arrives. The sensor's potential inability to detect the resulting wave the first time it travels over the sensor generates a delay, causing the location of impact to be inaccurate. Thus, while it is possible to calculate location using TDOA with piezoelectric or vibration sensors, the location calculation is prone to very low accuracy.
Another disadvantage of the use of TDOA to determine impact location is all vibration from an initial bullet impact must have dissipated before another bullet impact location can be determined. The wait time between shots can range from 0.5 seconds to 5 seconds depending on the target plate material and type of sensor used. As a result, TDOA cannot be used to detect the location of bullet impacts using a firearm with rapid fire capability.
Therefore, a need exists for a new and improved shooting target system that uses a dense array of inexpensive sensors that are protected from bullet strikes to calculate the point of impact of a projectile on a target. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the shooting target system according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of providing a shooting target system that detects and locates the impact of a bullet on the target.